1. Field of the Invention
This invention relates to oil-in-water (O/W) emulsifiers comprising palmitate-stearate compositions, methods of emulsifying, and the resultant emulsions.
2. Statement of Related Art
The stability, fineness and rheological behavior of O/W-emulsions are critically determined by the type and composition of the emulsifier. Among the emulsifiers used for the preparation of O/W-emulsions, fatty acid soaps are particularly important because of their high emulsifying power for all the usual liquid and semisolid oil and fat components, and because of their easy availability. Among the fatty acid soaps, the most suitable by virtue of their hydrophilicity are the soaps of technical stearic acids. In the cosmetics field, these stearate-based emulsions are also known as stearate creams.
The technical stearic acids most widely used as base materials for emulsifiers are mixtures of stearic acid and palmitic acid which are obained by the saponification of tallow and separation of the solid fatty acid fraction, known as "stearin". The "triple-pressed" stearins obtained in this way consist of 50 to 55% by weight palmitic acid, 40 to 45% by weight stearic acid and small amounts of myristic acid, pentadecanoic acid, heptadecanoic acid and oleic acid. Another grade of technical stearin is obtained by hardening, (i.e. by hydrogenation of the unsaturated fractions of tallow fatty acid). A stearin obtained in this way comprises 25 to 30% by weight palmitic acid, 60 to 65% by weight stearic acid and small amounts of myristic acid, pentadecanoic acid, heptadecanoic acid, oleic acid and arachic acid.
Although investigations have been conducted into the influence of the C.sub.16 /C.sub.18 -ratio of stearic acid/palmitic acid mixtures on the crystallization behavior and the physical-chemical properties of such mixtures, for example by Tillotson (J. SOC. COSMET. CHEM. 6, (1955), Pp. 40-49), nothing is known of the influence of the carbon-chain distribution of these fatty acids on the emulsifying power of the soaps obtainable therefrom.
O/W-emulsions are metastable systems consisting of a discontinuous (inner) oil phase and a continuous (outer) aqueous phase which are for a finite period of time stabilized by the interface-stabilizing effect of the emulsifier. In the event of prolonged storage, particularly at elevated temperature, systems such as these show a tendency towards coalescence of the oil droplets and phase separation. Accordingly, there is a continuing need to find emulsifiers which are capable of dispersing the oil phase very finely in the aqueous phase and which stabilize and emulsion for prolonged periods.
A review of McCutcheon's Emulsifiers & Detergents and Functional Materials (combined North American and International Editions) 1984 Annuals, MC Publishing Co., Glen Rock, N.J., U.S.A. (1984) indicates that several commercial products are available that contain palmitic and stearic acid derivatives, although the weight ratios of these components are not specified. Examples of such products are:
(a) "Tefose" 63 and 1500--a PEG (polyethylene glycol) palmito-stearate, nonionic base for O/W pharmaceutical ointments and lotions (a product of Gattefosse Corp., Hawthorne, N.Y., U.S.A); PA1 (b) "Tefose" 2000--a PEG palmito-stearate with ethoxylated fatty alcohol, nonionic base for O/W cosmetic and pharmaceutical lotions having an HLB of 10.2; PA1 (c) "Tefose" 2561--a glyceryl and PEG palmito-stearate with ethoxylated fatty alcohol, nonionic base for O/W pharmaceutical and cosmetic lotions and soft creams having an HLB of 10/11; PA1 (d) "Cutina" MD-A--a mixture of mono- and diglycerides of palmitic and stearic acids, a nonionic consistency-giving agent for O/W and W/O systems (a product of Henkel Corporation, Ambler, Penna., U.S.A. and Henkel KGaA, Duesseldorf, F.R. Germany); PA1 (e) glycerol stearate/palmitate, nonionic and anionic emulsifiers for food, cosmetics, and pharmaceuticals (products of Hefti, Ltd., Zurich, Switzerland); PA1 (f) "Imwitor" glycerol monodiesters of palmitic/stearic acids, nonionic stabilizer dispersing agent for foods and cosmetics, and anionic O/W emulsifier for cosmetics and food when containing 8% potassium distearate (a product of Dynamit Nobel AG, Troisdorf, F.R. Germany); and PA1 (g) "Teginacid" ML blend of mono- and diglycerides of palmitic and stearic acid with PEG (40) stearate, emulsifier for finely dispersed emulsions (a product of Th. Goldschmidt AG, Essen, F.R. Germany).
There is no indication in the above publication that any of the above products use a critical weight ratio of palmitic to stearic acids.